In the processing of crude oils prior to refinery separations, the presence of intractable emulsions often presents serious problems leading to oil losses, contamination problems, corrosion, fouling or plugging problems, and expensive environmental treatment/disposal costs. These emulsions often arise while producing the crude from its formation source, especially when the crude is a heavy crude having an API gravity of about 20 or less, and particularly those with an API gravity from 7 to 12. These crudes are specially hard to produce, and when produced are difficult to refine. Many produced crude oils also contain soluble inorganic salts, such as sodium chloride, calcium chloride, magnesium chloride or sulfate. The presence of such salts in a crude oil wreaks havoc to the processing of the oil in a refinery, causing severe corrosion, poor cracking yields, plugging and ultimately equipment failure. It is customary to "desalt" incoming crudes at a refinery by mixing the crude with wash water and allowing the water phase to dissolve out the salt and settle in a desalter vessel. These vessels are often arranged in series for multi-stage desalting. Electrical grids are usually provided in the settled oil layer to encourage and accelerate coalescence of the residual water droplets. Recent analysis work on heavy Canadian and Chinese crudes illustrates problems inherent with refining heavy crudes. An article in Oil & Gas Journal, Jan. 20, 1997, describes the composition of two somewhat typical heavy crude oils in great abundance, but did nothing to suggest the recovery and processing. One of the problems especially in the case of heavy crude oils involves contamination by heavy metals and undesirable organic compounds of oxygen, sulfur and nitrogen. These materials are usually intimately associated with the organic interfacial structures of emulsions, thus exacerbating the intractability of the emulsion and also causing corrosion and undesirable contamination in refinery processes.
Often obnoxious, hard to handle, heavy crude oil in many parts of the world is, therefore, deemed uneconomic to produce and refine. Thus, there is a need for oil emulsion breaking/separation technology suitable for use adjacent to heavy crude oil producing fields where the heavy crude oil exits from the producing well combined with considerable water and solids. This is particularly the case when high pressure steam or other media particularly surfactant solutions are injected into the producing formation for enhanced recovery of high density, high viscosity crude oils. The crude oil-water mixture flowing to the surface generally contains a considerable, even a large, portion of a difficult-to-separate emulsions of water-in-oil, or oil-in-water. Some of the waxes and bitumen present with the oil in the underground formation, as well as finely divided inorganic solids such as sands or clays which act as emulsion stabilizers, providing a shield at the oil-water interface which prevents the water droplets from coalescing. These intractable emulsions are a serious disposal problem and represent a great economic waste. While U.S. Pat. No. 4,938,876 describes a very successful and useful system for emulsion breaking in a refinery operation, these lightly viscous, high specific gravity crudes defy successful enhanced gravity separation for meaningful oil recovery.
In the processing of heavy crude oils as produced from their formations, it is increasingly common to encounter crudes with a large component of asphaltic or resinous material. Such crudes are particularly difficult to process due to high viscosity, high specific gravity and high contents of heavy metals and sulfur. In the prior art where high quality lubricating oils are produced from refined heavy-oil fractions, asphalt and resins are removed during the refining process by dissolving the whole fraction in a low-boiling solvent such as propane or butane and then heating the solution under pressure to a point approaching the critical temperature of the solvent at which the solvent power decreases, and the least desirable fractions of the oil are precipitated--namely the asphaltic and/or resinous components. This is satisfactory in the refinery environment but has heretofore not been attempted with a messy heavy crude oil.
Additionally, heavy crudes in many parts of the world characteristically are high in asphaltenes content making them difficult to use as a refinery feedstock. In many parts of the world, early production of heavy-asphalt containing crude oils were merely stripped of their lighter, more easily refined, fractions at the well-head with the environment bearing the brunt of the disposal of the unwanted heavy fractions. Further, other sources of crude oil which are difficultly produced are the tar sands found predominantly in Canada, where the solid materials are difficult to separate from the refinable crude and when separation is possible, create a significant disposal problem because of continuing contamination by the solids disposed.
It is accordingly an object of this invention to provide a process for treating these heavy crude oils to recover more refinable product and provide for environmentally-benign disposal of less-useful materials.
It is a further object of this invention to provide a process for pre-treating produced heavy crude oils to remove asphaltenes from the crude prior to entering the refinery process. It is yet a further object of this invention to provide a process for separating solid materials contaminating heavy crude oil as produced whereby the separated solids may be disposed of in an environmentally benign manner.
It is yet a further object of this invention to provide a process for breaking intractable emulsions occurring in produced crude such that a greater amount of refinable oil is recovered and entered into the refining process. It is an especially preferred objective of this invention to provide such process and system which can be located at the well-head on a pad or skid-mounted support such that unwanted materials can be separated from refinable crude prior to the transportation of such material to the refinery.
The foregoing and other advantageous objects of this invention may be accomplished by the invention as herein described.